Boron is a well known dopant used for modifying the conductivity of semiconductor materials in the manufacture of integrated electronic circuits. Monatomic boron ions (B+) are commonly implanted into silicon for this purpose. A typical ion source used for generating an ion beam containing monatomic boron ions uses BF3 gas as the feed gas to the usual plasma chamber of the ion source. In the ion source, the BF3 gas is disassociated in the plasma to form B+ ions, often as well as BF+ and BF2+. The ion beam extracted from the ion source is passed through a mass analyser to select the B+ ions for onward transmission for implanting in the semiconductor wafer target.
It is also known to use decaborane (B10H14) as a feed stock for an ion source in ion implantation. Decaborane is used to produce ions each comprising up to 10 boron atoms. Such BxHy+ ions can be used to implant boron atoms at relatively low energies.
Decaborane Ion Implantation by Perel et al, IIT 2000, pp. 304 to 307, discloses the spectrum of ion masses which may be generated from a suitably controlled ion source employing decaborane as feed stock. Ions having masses corresponding to the presence of 10 boron atoms are selected in a mass analyser for implantation.
U.S. Pat. No. 6,288,403 discloses an ion source adapted for the preferential production of decaborane ions, particularly for low energy implantation.